Design of hydrophobic polydimethylsiloxane and polybenzoxazine hybrids for interlayer low k dielectrics†
The continual development of the microelectronic industry demands the most desirable low dielectric materials with high thermal stability. In this work, to design the low k materials, the following methods have been utilized viz., (i) benzoxazine monomers from aromatic and aliphatic diamines, (ii) variation of the chain length of nonpolar aliphatic diamines [(CH2)2, (CH2)4, (CH2)6], and (iii) an incorporation of polydimethylsiloxane (PDMS). The variation in chemical structure and dielectric properties of modified polybenzoxazine (PBz) have been investigated by these phenomenological approaches. High resolution transmission electron microscopy (HRTEM) images clearly indicate the layer-by-layer arrangement of hybrid PDMS–PBz matrices. Frequency dependent dielectric spectra ascertain the decreased trend in the value of dielectric constant as well as dielectric loss. It is found that 1,6-diaminohexane–polydimethylsiloxane–polybenzoxazine (DAH–PDMS–PBz) hybrid matrix exhibits the lowest dielectric constant of 2.42 at 1 MHz. An interesting structural feature which led to reducing the dielectric constant were high volume fraction of intramolecular hydrogen bonding, nonpolar aliphatic long chain, and the existence of a distinct layer-by-layer arrangement in the PDMS–PBz matrix. In addition, the presence of thermally stable Si and flexible Si–O–Si linkages enhanced the thermal stability and flexibility of thermosetting polybenzoxazine hybrid matrices. From these observations it can be concluded that the structural modification can be achieved by using the above methods to obtain low k hybrid materials.